Better branch management in existing repositories

Detect 'IgnoreBranches' setting value to set for already existing repositories

when the value of the setting is not set
and depending of the number of Tfs remotes initialized.
if at least 2 tfs remotes, then we want to support branches
otherwise, ignoring them...
hmmm....no :(
This is the most important line of this PR (and the only reason of this PR).
The goal is to set automatically the better value for the setting `GitTfsConstants.IgnoreBranches` for already cloned repositories with an earlier version of git-tfs. For that, we count the existing tfs remotes. If there is only one, we could be pretty sure that the user don't want to support branches. Otherwise, we are sure that the user want to support branches.